Final answer:
The correct inference to make when Vesa saw water turn to ice after cooling is that the water froze, which is a physical process occurring at temperatures below 0°C.
Step-by-step explanation:
When Vesa noticed that the water outside turned to ice after the temperature became cooler, based on this observation, we can make the inference that (b) the water froze. This is a basic physical process where water turns into ice at temperatures below 0°C. During the freezing process, the heat is absorbed by the ice, providing the energy required to partially overcome the attractive forces in the solid, until a phase transition to solid ice occurs. The temperature does not change during the phase transition itself as observed in experiments where the temperature of the water remains constant at 0°C until all ice has melted or formed depending on the direction of the phase change.